THE INACTIVATION OF PLACENTAL TOXIN BY HUMAN SERUM

Abstract

Placental tissue was perfused with saline, dried and stored as a source of toxin. Saline extracts which were prepared from the dried material were assayed by intravenous injn. into mice. When serum was added to samples of the extracts in vitro, the toxic-ity gradually decreased to a new, lower level at which some of the toxicity still remained. The decrease of toxic activity was approx. proportional to the logarithm of the concn. of serum. With a constant concn. of serum, a somewhat greater % of toxin was inactivated in weaker toxic extracts than in stronger toxic extracts. When a 2d addition of serum was carried out, the toxic activity fell to a still lower level. If the original toxicity was restored by addition of further toxin, the toxic level then remained at full strength. The process was temp. sensitive, the % inactivation in 4 hrs. being trebled between 5-15[degree]C. The same final toxic levels were reached within 2 hrs. at different temps. between 20-40[degree]C. One unit of inactivating potency is defined as that amt. which will inactivate a standard toxic placental extract (20 MLD/ ml.) to half strength. The inactivating potency of a given serum is then, in units, the reciprocal of the serum concn. (i.e., the dilution) that inactivates a standard extract to half strength.